1. Field of the Invention
The present invention relates to a printer and, more particularly, to a wheel printer incorporating improvements for preventing free movement of a wheel case containing a print wheel.
2. Description of Related Art
A wheel printer is provided, as shown in FIG. 5, with a platen 20 extended in a horizontal position, a carriage 30 supported on a guide shaft 14 parallel to the platen 20, a guide member 15 for movement along the platen 20, and a wheel cassette 36 consisting of a print wheel 34 and a wheel case 35 containing the print wheel 34. The carriage 30 carries a type striking mechanism, not shown, a ribbon cassette 37, and a wheel holder for detachably holding the wheel cassette 36. Shown also in FIG. 5 are a side frame 11, a bottom plate 12, a carriage body 31, a ribbon guide 33 and a paper guide 32.
The wheel holder will be described. A motor holder 40 holding a wheel driving motor, not shown, is supported swingably on the guide shaft 14 by a connecting plate 41 fixed thereto. A spindle 45 is supported in a sleeve 44 fixed to the motor holder 40. A gear member 43 having a gear 43a engaging a driving gear fixed to the output shaft of the wheel driving motor is mounted fixedly on the spindle 45. The spindle 45 has an interlocking portion 46 that engages the center hole of the print wheel 34 in its free end. The motor holder 40 has a support wall 51 for supporting the wheel case 35 at its lower end, a holding wall 49 for pressing the wheel case 35 with a rubber presser 48 that comes into contact with the front surface of the wheel case 35, and positioning walls, not shown, to position the wheel case 35 with respect to the horizontal direction. The ribbon guide 33 has a contact protrusion 50 that touches an upper portion of the back surface of the wheel case 35. The carriage body 31 has a back wall 100 having a positioning portion 101. The support wall 51 of the motor holder 40 snaps over the positioning portion 101 when pivoted into a work position as shown in dotted lines in FIG. 5. The back surface of the wheel case 35 is spaced from the back wall 100 of the carriage body 31.
To enable the wheel cassette 36 to be inserted in and removed from the wheel holder, the motor holder 40 and the associated parts can be shifted between a working position indicated by dot-dash-dot lines in the lower portion of FIG. 5 to hold the wheel cassette 36 for printing and a releasing position indicated by alternate long and two short dashed lines in the upper portion of FIG. 5. The cassette shown in solid lines is shown in a partially inserted position. The motor holder 40 is turned away from the platen 20 by an angle of about 20.degree. on the guide shaft 14 to shift the same from the working position to the releasing position. The wheel cassette 36 can be inserted in or removed from the wheel holder with the motor holder 40 positioned at the releasing position. A plate spring 102 is attached to the lower end of the paper guide 32 to bias the wheel case 35 resiliently toward the motor holder 40 to restrain the wheel case 35 from free movement and vibration.
Without the plate spring 102, the wheel case 35 is caused to play or vibrate by vibrations generated by the rotation of the print wheel 34 and the movement of the carriage 30 because the upper portion of the wheel case 35 is held between the holding wall 49 and the contact protrusion 50, and a small gap is formed between the lower portion of the back surface of the wheel case 35 and the positioning portion 101 of the back wall 100.
Although the play and vibration of the wheel case 35 during printing operation can be prevented by the plate spring 102, the lower portion of the wheel cassette 36 is biased excessively toward the front, i.e., toward the motor holder 40, by the plate spring 102 as indicated by continuous lines in inserting the wheel cassette 36 in the wheel holder, and the upper end of the ribbon guide 33 touches the wheel case 35 as shown in FIG. 5 to impede the movement of the wheel cassette 36.